Method and means for coding and rebuilding that data contents of unavailable DASDs or rebuilding the contents of DASDs in error in the presence of reduced number of unavailable DASDs in a DASD array

摘要

A method and means for coding an (M-1)M data array written onto an array of M synchronous recording paths and for rebuilding and writing onto spare recording path capacity when up to a preselected number R of array DASDs fail, or one DASD becomes erroneous and up to R-2 fail. Data is mapped into the parallel paths using an (M-1)M data and parity block array as the storage model where M is a prime number and each block extent is uniform and at least one bit in length. The (M-1) M data and parity block array is encoded to include zero XOR sums along a traverses of slopes 0, 1, 2, . . . , P-1, extended cyclically over said data array. Rebuilding data and parity blocks is occasioned upon unavailability of no more than R less than or equal to P recording path failures, or one recording path in error and up to R-2 recording path failures. This includes calculating XOR-sums along the traversed paths of P-1 slopes, cyclic and linear shifts and XOR operations, recovering the unavailable DASDs by means of iterative solution of a set of recursions, and finally writing the rebuilt array back to onto M recording paths inclusive of any spare paths.